package org.apache.lucene.index;

import org.apache.lucene.store.Directory;
import org.apache.lucene.store.InputStream;
import org.apache.lucene.store.OutputStream;
import org.apache.lucene.store.Lock;

import java.util.HashMap;
import java.io.IOException;


/**
 * 复合文件读
 * Class for accessing a compound stream.
 * This class implements a directory, but is limited to only read operations.
 * Directory methods that would normally modify data throw an exception.
 *
 * @author Dmitry Serebrennikov
 * @version $Id: CompoundFileReader.java,v 1.7 2004/07/12 14:36:04 otis Exp $
 */
class CompoundFileReader extends Directory {

  private static final class FileEntry {
    long offset;
    long length;
  }


  // Base info
  private Directory directory;
  private String fileName;

  // Reference count
  private boolean open;

  private InputStream stream;
  private HashMap entries = new HashMap();


  public CompoundFileReader(Directory dir, String name)
    throws IOException {
    directory = dir;
    fileName = name;

    boolean success = false;

    try {
      stream = dir.openFile(name);

      // read the directory and init files
      int count = stream.readVInt();
      FileEntry entry = null;
      for (int i = 0; i < count; i++) {
        long offset = stream.readLong();
        String id = stream.readString();

        if (entry != null) {
          // set length of the previous entry
          entry.length = offset - entry.offset;
        }

        entry = new FileEntry();
        entry.offset = offset;
        entries.put(id, entry);
      }

      // set the length of the final entry
      if (entry != null) {
        entry.length = stream.length() - entry.offset;
      }

      success = true;

    } finally {
      if (!success && (stream != null)) {
        try {
          stream.close();
        } catch (IOException e) {
        }
      }
    }
  }

  public Directory getDirectory() {
    return directory;
  }

  public String getName() {
    return fileName;
  }

  public synchronized void close() throws IOException {
    if (stream == null)
      throw new IOException("Already closed");

    entries.clear();
    stream.close();
    stream = null;
  }

  public synchronized InputStream openFile(String id)
    throws IOException {
    if (stream == null)
      throw new IOException("Stream closed");

    FileEntry entry = (FileEntry) entries.get(id);
    if (entry == null)
      throw new IOException("No sub-file with id " + id + " found");

    return new CSInputStream(stream, entry.offset, entry.length);
  }

  /**
   * Returns an array of strings, one for each file in the directory.
   */
  public String[] list() {
    String res[] = new String[entries.size()];
    return (String[]) entries.keySet().toArray(res);
  }

  /**
   * Returns true iff a file with the given name exists.
   */
  public boolean fileExists(String name) {
    return entries.containsKey(name);
  }

  /**
   * Returns the time the named file was last modified.
   */
  public long fileModified(String name) throws IOException {
    return directory.fileModified(fileName);
  }

  /**
   * Set the modified time of an existing file to now.
   */
  public void touchFile(String name) throws IOException {
    directory.touchFile(fileName);
  }

  /**
   * Removes an existing file in the directory.
   */
  public void deleteFile(String name) {
    throw new UnsupportedOperationException();
  }

  /**
   * Renames an existing file in the directory.
   * If a file already exists with the new name, then it is replaced.
   * This replacement should be atomic.
   */
  public void renameFile(String from, String to) {
    throw new UnsupportedOperationException();
  }

  /**
   * Returns the length of a file in the directory.
   */
  public long fileLength(String name)
    throws IOException {
    FileEntry e = (FileEntry) entries.get(name);
    if (e == null)
      throw new IOException("File " + name + " does not exist");
    return e.length;
  }

  /**
   * Creates a new, empty file in the directory with the given name.
   * Returns a stream writing this file.
   */
  public OutputStream createFile(String name) {
    throw new UnsupportedOperationException();
  }

  /**
   * Construct a {@link Lock}.
   *
   * @param name the name of the lock file
   */
  public Lock makeLock(String name) {
    throw new UnsupportedOperationException();
  }

  /**
   * Implementation of an InputStream that reads from a portion of the
   * compound file. The visibility is left as "package" *only* because
   * this helps with testing since JUnit test cases in a different class
   * can then access package fields of this class.
   */
  static final class CSInputStream extends InputStream {

    InputStream base;
    long fileOffset;

    CSInputStream(final InputStream base, final long fileOffset, final long length)
      throws IOException {
      this.base = base;
      this.fileOffset = fileOffset;
      this.length = length;   // variable in the superclass
    }

    /**
     * Expert: implements buffer refill.  Reads bytes from the current
     * position in the input.
     *
     * @param b      the array to read bytes into
     * @param offset the offset in the array to start storing bytes
     * @param len    the number of bytes to read
     */
    protected void readInternal(byte[] b, int offset, int len)
      throws IOException {
      synchronized (base) {
        long start = getFilePointer();
        if (start + len > length)
          throw new IOException("read past EOF");
        base.seek(fileOffset + start);
        base.readBytes(b, offset, len);
      }
    }

    /**
     * Expert: implements seek.  Sets current position in this file, where
     * the next {@link #readInternal(byte[], int, int)} will occur.
     *
     * @see #readInternal(byte[], int, int)
     */
    protected void seekInternal(long pos) throws IOException {
    }

    /**
     * Closes the stream to futher operations.
     */
    public void close() throws IOException {
    }

  }
}
